As shown in FIGS. 1 and 2, an electron beam irradiating device 1 includes an electron beam generation source 2, a vacuum chamber 3 which surrounds the electron beam generation source 2, and an electron beam exit window 4 attached to the vacuum chamber 3. The wall surface of the vacuum chamber 3 is partially cut away, and the electron beam exit window 4 is provided to this portion from which the wall surface is cut away. That is, a closed space is formed by the vacuum chamber 3 and the electron beam exit window 4. A vacuum pump P is connected to the vacuum chamber 3. The closed space can be brought into a vacuum state by the vacuum pump P. The electron beam exit window 4 includes a window foil which allows an electron beam B to pass therethrough. An electron beam generated from the electron beam generation source 2 exits the vacuum chamber 3 through this window foil. Reference numeral 5 in FIG. 1 and FIG. 2 denotes an extraction electrode for extracting electrons excited in the electron beam generation source 2.
The inside of the vacuum chamber 3 is evacuated by the vacuum pump P. At this point of operation, the window foil functions as a partition wall between a vacuum atmosphere and the atmosphere and hence, an atmospheric pressure is applied to the window foil. In addition, the window foil is formed with a small thickness of approximately several μm to 10 μm in order to increase transmissivity of the electron beam B. Further, the window foil absorbs a part of the electron beam B, thus generating heat. Accordingly, the window foil significantly deteriorates compared with other components of the apparatus, thus easily causing a trouble. For this reason, the window foil may be periodically replaced even if there is no malfunction or a problem caused by deterioration.
For example, patent literature 1 discloses the configuration where a window foil is attached to an electron beam irradiating device. Patent literature 1 discloses the following configuration. A grid is attached to a vacuum chamber, the surface of the grid has an annular groove, a window foil is made to overlap with the annular groove in a state where an O-ring is disposed in the annular groove, a pressing member is further made to overlap with the window foil, and the grid and the pressing member are fastened to each other with bolts, thus attaching the window foil to the electron beam irradiating device. With such a configuration, gas sealing property in the vacuum chamber can be ensured, and the window foil can be easily replaced by loosening the bolts and by removing the pressing member.